U.S. Pat. No. 6,044,163 discloses a hearing aid comprising an input transducer, an amplifier and transmission circuit, an output transducer and a calculating unit working according to the principle of a neural structure. The calculating unit performs a classification in order to modify the transmission characteristics in dependence on the auditory situation. The training is distinguished between, firstly, a non-supervised training, which occurs according to a predetermined matrix only upon evaluation of an event signal generated by the calculating unit, and, secondly, a supervised training where a matching module evaluates a desired target reply in addition to the event signal. The US patent provides an approach using a neural structure, which may be trained during the operating mode. However, since the disclosed neural structure comprises a multi-layer neural network an intensive calculation in order to update the neuron weights is required.
International patent application WO 2004/056154 discloses a hearing device having an input transducer, an output transducer, and signal processing means for influencing a signal in the hearing device in accordance with a processing parameter set (PPS). A PPS memory accessible by the signal processor means stores a number of different PPS's for use by the signal processing means. The system further has means for monitoring the acoustic environment in a learning mode, where the user selects a PPS. Later in an automatic mode the hearing device selects a PPS based on a comparison between the current acoustic environment and the monitored environment in the learning phase. This hearing device discloses a classification system where the most representative characterizing acoustic values are calculated for each PPS. However, the performance may decrease, if a PPS has to be used for different characterizing acoustic values. That is, according to this hearing device a characterizing acoustic value matches a similar PPS.